Vehicles may be fitted with evaporative emission control systems such as onboard fuel vapor recovery systems. Such systems capture and reduce the release of vaporized hydrocarbons (HCs), such as fuel vapors released from a vehicle gasoline tank during refueling, to the atmosphere. Specifically, the vaporized HCs are stored in a fuel vapor canister packed with an adsorbent that adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system purges the vapors into an engine intake manifold for use as fuel. The evaporative emissions system may include an ejector system, one more check valves, and/or one or more controller-actuatable valves for facilitating vapor purge under boosted or non-boosted engine operation.
Various approaches have been developed to diagnose and detect degradation in ejector system components adjacent to ejector inlets and/or upstream of the ejector inlets. However, such approaches fail to diagnose or detect degradation in the ejector system downstream of an ejector outlet. For example, a high load purge line may be used to couple the ejector outlet to an air intake system (AIS) of the engine at a position upstream of a compressor. During purge under high load operation (e.g., when the engine is under boost conditions), vapors may be routed to the engine intake via the high load purge line. If the high load purge line degrades, any resulting undesired evaporative emissions may go undetected.
The inventors herein have recognized the above-mentioned disadvantages and have developed a dual path purge system for an engine. In one example approach, a method is provided, comprising, in a first condition, purging fuel vapors from a fuel vapor canister through an ejector unit into an air intake system of an engine without simultaneously conducting a test for undesired evaporative emissions on a high load purge line coupled between the ejector unit and the air intake system; and in a second condition, purging fuel vapors from the fuel vapor canister while simultaneously conducting the test for undesired evaporative emissions on the high load purge line.
As one example, in the first condition, vapors may be purged from the fuel vapor canister under both boost and manifold vacuum conditions. In the second condition, fuel vapors may be purged from the fuel vapor canister under natural aspiration conditions but not boost conditions. In the second condition, a check valve mounted at the connection of the AIS and the high load purge line that opens during boost and closes under manifold vacuum conditions enables vacuum to be drawn on the high load purge line, which in turn enables the test for undesired evaporative emissions on the high load purge line to be performed. Furthermore, the check valve enables the high load purge line diagnostic test to be performed during canister purging, which reduces the disruption of engine operation by evaporative emissions system diagnostic tests. As an additional advantage, the check valve prevents the flow of unmetered air through the ejector during natural aspiration.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.